The present invention is directed to an endless flexible seamed belt having improved seam quality and smoothness with a low thickness differential between the seamed portion of the belt and the adjacent portions of the belt.
Perhaps, the most important invention that may have ever been made was that of the wheel. Arguably, one of the follow-on inventions of almost equal importance was directed to a belt. Initially, the belts were fabricated by taking two ends of a web material and fastening them together by a variety of techniques such as sewing, wiring, stapling, providing adhesive joints, etc. While such joined or seamed belts are suitable for many applications, such as the delivery of rotary motion from a source such as a motor, to implement a device such as a saw blade, they are not as satisfactory in many of the more sophisticated applications of belt technology in common practice today. In the technology of the current day many applications of belts require much more sophisticated qualities and utilities and in particular for such special applications as in electrostatographic and electrographic imaging apparatus and processes for use as photoreceptors, intermediate sheet and/or image transport devices, fusing members or transfix devices, it is ideal to provide a seamless belt whereby there is no seam in the belt which mechanically interferes with any operation that the belt performs or any operation that may be performed on the belt. While this is ideal the manufacture of seamless belts requires rather sophisticated manufacturing processes which are expensive and are particularly more sophisticated, difficult and much more expensive for the larger belts. As a result, various attempts have been made to provide seamed belts which can be used in these processes. Previous attempts to manufacture seamed belts have largely relied on belts where the two ends of the belt material have been lapped or overlapped to form the seam or have butted against one another and then fastened mechanically by heat or other means of adhesion such as by the use of an adhesive or ultrasonic welding.
The belts formed according to the typical butting technique while satisfactory for many purposes are limited in bonding, strength and flexibility because of the limited contact area formed by merely butting or overlapping the two ends of the belt material. Furthermore, belts formed according to the butting or overlapping technique provide a bump or other discontinuity in the belt surface leading to a height differential between adjacent portions of the belt of 0.010 inches or more depending on the belt thickness, which leads to performance failure in many applications. For example, one of the most severe problems involves cleaning the imaging belt of residual toner after transfer of the toner image. Intimate contact between the belt and cleaning blade is required. With a bump, crack or other discontinuity in the belt the tuck of the blade is disturbed which allows toner to pass under the blade and not be cleaned. Furthermore, seams having differential heights may when subjected to repeated striking by cleaning blades cause the untransferred, residual toner to be trapped in the irregular surface of the seam. Photoreceptors which are repeatedly subjected to this striking action tend to delaminate at the seam when the seam is subjected to constant battering by the cleaning blade. As a result, both the cleaning life of the blade and the overall life of the photoreceptor can be greatly diminished as well as degrading the copy quality. In addition, such irregularities in seam height provide vibrational noise in xerographic development which disturbs the toner image on the belt and degrades resolution and transfer of the toner image to the final copy sheet. This is particularly prevalent in those applications requiring the application of multiple color layers of liquid or dry developer on a photoreceptor belt, which are subsequently transferred to a final copy sheet.
In these sophisticated applications, it is desired to provide a seam height differential between the seam and the unseamed adjacent portions less than 0.001 inch. In addition, the presence of the discontinuity in belt thickness reduces the tensile strength of the belt which for prolonged use is desirably 80-90% that of the parent material unseamed. Furthermore, it is desired that the seamed belt have seam mechanical bonding, strength and flexibility capable of satisfactory performance for at least 500,000 cycles. In addition, the discontinuity or bump in such a belt may result in inaccurate image registration during development, inaccurate belt tracking and overall deterioration of motion quality, as a result of the translating vibrations.
While the above-identified cross-referenced applications deal with sophisticated techniques wherein it is desired to provide a seam height differential between the seam and the unseamed adjacent portions less than 0.001 inch, there are, however many less sophisticated applications wherein a seamed belt having a seam height differential less than the combined thicknesses of two ends of the belt is entirely adequate and it is to that embodiment that the particular invention described herein is directed. Such applications may include photoreceptor belts, fusing belts, intermediate and transfer belts for xerographic applications, transport belts for document and paper handling belts.